1. Field of the Invention
The present invention relates to a fan filter unit to be installed in cleanrooms of factories for manufacturing semiconductor devices, liquid-crystal panels, and films and more particularly, to a fan filter unit comprising a ventilation fan and dust and chemical filters incorporated into an enclosure, which removes efficiently dust and chemical substance existing in the atmosphere of a cleanroom by the chemical and dust filters and which enables energy saving of the fan and reduction of the air circulating space.
2. Description of the Related Art
To maintain the cleanliness of air in the cleanroom at a specific level, typically, cleanroom systems have been used. For example, whole laminar flow type cleanroom systems have been used for this purpose, which comprise fan filter units of this sort arranged on the whole ceiling surface of the cleanroom. FIG. 1 schematically shows the configuration of an example of the prior-art cleanroom systems of this sort.
The prior-art cleanroom system 100 shown in FIG. 1 comprises a cleanroom 140, a ceiling chamber 147 formed over the cleanroom 140, fan filter units 142 arranged in a matrix array on the whole ceiling surface 140a of the cleanroom 140, an underfloor region 144 defined by floor panels 143 arranged on the floor of the cleanroom 140, a cooling coil 145 for air-temperature control mounted in the region 144, and an air circulation path 146 that connects the region 144 with the chamber 147. Each of the fan filter units 142 includes a ventilation fan 148 and a dust filter 141. Each of the floor panels 143 has a punched or perforated structure that allows the air to penetrate.
With the prior-art cleanroom system 100 shown in FIG. 1, the air existing in the ceiling chamber 147 is introduced into the inside of the fan filter units 142 by their fans 148. The air thus introduced is passed through the filters 141 to be cleaned by the same. The air thus cleaned or filtered is emitted or blown to the inside of the cleanroom 140. At this time, the cleaned air emitted from the units 142 form a vertical laminar flow of air that heads for the floor panel 143 from the ceiling surface 140a of the cleanroom 140. The cleaned air thus emitted into the cleanroom 140 flows vertically into the underfloor region 144 through the floor panels 143 and then, returns to the ceiling chamber 147 through the cooling coil 145 and the circulation path 146. Thereafter, the air thus returned to the chamber 147 is introduced into the cleanroom 140 again.
Through the above-described processes, the clean air is repeatedly circulated in the cleanroom system 100. The cooling coil 145 serves to decrease the thermal load of the circulating air and therefore, the clean air with a fixed temperature is always supplied to the cleanroom 140. Also, since the vertical laminar flow of the air is formed in the cleanroom 140, the inside of the cleanroom 140 can be maintained at a specific high cleanliness level.
The Japanese Non-Examined Patent Publication No. 9-287791 published in November 1997 discloses a cleanroom system having approximately the same configuration as that shown in FIG. 1.
Although the above-described cleanroom system 100 makes the cleanroom 140 highly clean, there is an anxiety that defects occur in the product due to contamination induced by chemical substance existing in the atmosphere in the leading-edge manufacturing processes for highly miniaturized products such as ultralarge-scale integrated circuits (ULSIs). To cope with the anxiety, fan filter units having chemical filters have been developed and used, an example of which is shown in FIG. 2.
The prior-art fan filter unit 250 shown in FIG. 2 comprises an enclosure or casing 252 having a first cylindrical part 252a and a second cylindrical part 252b that are coaxially connected together. The first part 252a is smaller in size than the second part 252b. The bottom end of the first part 252a is connected to the top end of the second part 252b. The inner space of the first part 252a communicates with the inner space of the second part 252b. 
An air inlet 252c is formed at the top end of the first part 252a. A ventilation fan 253 is mounted in the first part 252a. The fan 253 is driven by a motor (not shown) provided in the part 252a. An air outlet 252d is formed at the bottom end of the second part 252b. A dust filter 254 for removing dust or particles and a chemical filter 251 for removing chemical substance are mounted to be vertically apart from each other in the second part 252b. The dust filter 254 is fixed to the bottom end of the second part 252b so as to close the air outlet 252d. The chemical filter 251 is fixed to the inner wall of the second part 252b over the dust filter 254 at a specific distance. A partition plate 255 having holes 255a in its peripheral area is fixed to the inner wall of the second part 252b over the chemical filter 251 at a specific distance. The plate 255 divides the inner space of the enclosure 252 into upper and lower ones. The upper and lower spaces thus divided are connected to each other through the holes 255a of the plate 255.
With the prior-art fan filter unit 250 shown in FIG. 2, the outside air 261 existing in the outside of the unit 250 is introduced into the enclosure 252 through the air inlet 252c, forming the air 262. The air 262 thus introduced into the enclosure 252 flows to reach the chemical filter 251 through the holes 255a of the partition plate 255. The chemical filter 251 removes chemical substances contained in the air 262, forming the chemical-removed air 263. The air 263 thus filtered further flows to the dust filter 254 and penetrates the same. The dust filter 254 removes dust or particles contained in the air 263. As a result, the purified air 264 is emitted from the outlet 252d of the enclosure 252 to the outside of the unit 250.
The prior-art unit 250 shown in FIG. 2 can be used as the fan filter unit 142 of the prior-art cleanroom system 100 shown in FIG. 1. In this case, the concentration of chemical substance existing in the atmosphere of the cleanroom 140 can be lowered, because the unit 250 includes the chemical filter 251. To further decrease the concentration of chemical substance in the cleanroom 140, there is the need to increase the flow rate of the purified air 264 emitted from the unit 250, thereby raising the flow rate of the air 262 that penetrates the chemical filter 251.
However, if the flow rate of the purified air 264 emitted from the unit 250 is increased, the overall amount of the circulating air within the cleanroom system 140 increases. This raises a problem that the air circulating space (i.e., the air circulation path 146 and the ceiling chamber 147) needs to be expanded.
Also, to allow the increased circulating air to penetrate the path 146 and the air-cooling coil 145, the fan 253 needs to provide higher static pressure. Thus, there is a problem that electric power consumption of the motor for driving the fan 253 is raised.
Accordingly, an object of the present invention is to provide a fan filter unit that decreases efficiently the concentration of chemical substance existing in the atmosphere while the expansion of the air circulating space and the electric power consumption increase of the fan-driving motor are suppressed.
The above object together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A fan filter unit according to the present invention comprises:
an enclosure having an air inlet through which an outside air is introduced into the enclosure and an air outlet through which a cleaned air is emitted or discharged from the enclosure;
a chemical filter mounted in the enclosure to remove chemical substance existing in the outside air;
a dust filter mounted in the enclosure to remove dust existing in the outside air;
a fan mounted in the enclosure to introduce the outside air into the enclosure through the air inlet and to emit the cleaned air to outside of the enclosure; and
a bypassing path for returning part of the outside air that has penetrated the chemical filter to an upstream side of the fan without penetrating the dust filter.
With the fan filter unit according to the present invention, the bypassing path is provided for returning part of the outside air that has penetrated the chemical filter to an upstream side of the fan without penetrating the dust filter (i.e., without passing through the air circulating space and the air cooling coil). Thus, the necessary pressure loss occurring in the circulation of the outside air through the dust filter and other necessary members such as floor panels, a cooling coil, and an air circulating space can be reduced. As a result, the electric power consumption increase of the fan-driving motor can be suppressed.
Moreover, since the amount of the air penetrating the chemical filter is increased without increasing the overall amount of the air that is circulated in the cleanroom, the concentration of chemical substance existing in the atmosphere of the cleanroom can be decreased while the expansion of the air circulating space can be suppressed.
In a preferred embodiment of the unit according to the invention, a damper is further provided in the bypassing path for adjusting the amount of the outside air returned to the upstream side of the fan. In this case, it is preferred that the dumper is adjusted in such a way that the velocity of the air at the air outlet of the enclosure is set at a specific value.
In another preferred embodiment of the unit according to the invention, a sensor or detector is further provided for sensing or detecting the concentration of chemical substance existing in the air, in which the damper is controlled on the basis of the result of sensing or detection. In this case, it is preferred that the sensor or detector is used to sense or detect the concentration of chemical substance existing in the air in a cleanroom itself or in an air circulating space of a cleanroom.